Shortened folded monopole with radiation efficiency increased by ferrite loading



Dec. 27, 1966 R. c. FENWICK ET AL 3,295,137

SHORTENED FOLDED MONOPOLE WITH RADIATION EFFICIENCY INCREASED BY FERRITELOADING Filed Sept. 8. 1964 2 Shets-Sheet 1 FIG 3 INVENTORS RICHARD C.FENWICK WALTER L. WEEKS ATTORNEY Dec. 27, 1966 R. c FENWICK ETAL3,295,137

SHORTENED FOLDED MONOPOLE WITH RADIATION EFFICIENCY INCREASED BY FERRITELOADING Flled Sept 8, 1964 2 Sheets-Sheet 2.

FIG 4 FERRITE ON GROUNDED LEG FERRITE ON DRIVEN LEG /A'\NO FERRITE FIG 5mo mwZmumm FREQUENCY MC INVENTORS RICHARD C. FENWICK WALTER L WEEKSATTORNEY United States Patent SHORTENED FOLDED MONOPOLE WITH RADIA- TIONEFFICIENCY INCREASED BY FERRITE LOADING Richard C. Fenwick, Richardson,Tex., and Walter L. Weeks, Lafayette, Ind., assignors to Collins RadioCompany, Cedar Rapids, Iowa, a corporation of Iowa Filed Sept. 8, 1964,Ser. No. 394,979 2 Claims. (Cl. 343-787) This invention relates ingeneral to antennas and in particular to a means for increasing theeificiency and decreasing the length of an antenna structure.

Antenna structures are often very large. For example, a folded monopolegenerally is one-quarter wave length in height and for lower frequenciessuch a structure can be a hundred feet or more.

The present invention comprises an antenna in which the height may bereduced to a fraction of what it would normally be while stillmaintaining good efficiency.

A feature of this invention is found in the provision for an antennawhich has been partially surrounded by magnetic material.

Another object of this invention is to provide an increased efiiciencyshortened folded monopole.

Yet another object of this invention is to provide means for shorteningand increasing the efiiciency of an antenna.

Further objects, features, and advantages of this invention will becomeapparent from the following description and claims when read in view ofthe drawings, in which:

FIGURE 1 illustrates a folded monopole with one end connected to theground plane;

FIGURE 2 illustrates a folded monopole according to this invention withthe grounded end surrounded by magnetic material;

FIGURE 3 illustrates a folded dipole surrounded by suitable magneticmaterial;

FIGURE 4 illustrates a folded tripole antenna; and

FIGURE 5 is a plot of characteristics of an antenna.

When the length of a folded monopole is short as measured in wavelength,current in the two legs of the monopole is substantially equal andlittle radiation occurs. Under such circumstances the small amount ofradiation obtained results from the loop formed between the two legs ofthe monopole and is in the direction of the plane of the two legs. Whenthe height of the monopole is substantial, measured in wavelengths, theradiation efficiency is quite good because of the difference in currentflow or phase of the signal in the different legs. The present inventionobtains the advantage of the difference in phase in a structure that isrelatively short as measured in wavelengths by surrounding the groundedleg by ferromagnetic toroids.

A folded monopole is a well-known radiating structure. Such a monopoleis shown in FIGURE 1 which illustrates a ground plane to which the outerconductor 11 of cable 12 is connected. The inner conductor 13 of theconductor 12 comprises a first portion 14 and a second portion 15connected together by a joining portion 16. The end 17 of the portion 15is connected to the ground plane. The lengths of portions 14 and 15 aregenerally one-quarter wavelength at the desired operating frequency. Asfrequency is lowered, one quarter wavelength becomes impracticallylarge. However, a structure appreciably shorter than one-quarterwavelength is very inefiicient and the input impedance is usuallyunfavorable.

It has been discovered that by adding a number of ferrite disks aboutthe grounded leg 15 the radiation efficiency ice can be maintained highwhen the legs 14 and 15 are only one-thirtieth of a wavelength inheight.

FIGURE 2 shows such a structure. A plurality of toroid disks 18 aremounted about the grounded leg 15. In addition to lowering the resonantfrequency of the structure the ferrite toroids cause the currents to bereduced between the grounded leg and the driven leg, thereby increasingthe radiation.

FIGURE 3 illustrates a folded dipole 26 connected to a generator 21 byfeedlines 22 and 23 and coupling sections 24 and 25. The radiatingportion 26 of the dipole is surrounded by ferrite toroids 27.

FIGURE 4 illustrates a folded tripole antenna. This antenna comprisesthree insulated legs 30, 31 and 32 which support thereon ferrite disks33. A center cylindrical structure 34 extends through the disks 33 andis formed with a conical lower portion 36 which is electricallyconnected to the inner conductor 37 of a feedline 38. The outerconductor 39 is connected to the ground plane 35 and leads 40, 41 and 42extend from the top 43 of the cylindrical member 34 to the ground plane35. In a particular structure tested, the outside diameter of the disks33 was two feet and their total thickness was eight inches. The heightof the insulating support members 30, 31 and 32 was two feet so as toobtain an antenna 32 inches from the ground plane and 24 inches indiameter. In such a structure, the radiation efiiciency wassubstantially increased over a cylindrical radiator without the ferritedisks.

FIGURE 5 is a graph showing the increased efficiency using the structureshown in FIGURE 2. For the par ticular structure plotted, the height ofthe monopole was 40 inches and the outside diameter of the ferritemembers 18 on the grounded leg 15 was 2 /2 inches. In FIGURE 5 frequencyis plotted against received decibels. It is to be noted that curve A forthe structure shown in FIGURE 2 gives a substantially higher efiiciencythan curve B showing a monopole of the same size with no ferrite aboutthe grounded leg. Curve C illustrates ferrite about the driven leg 14.It is to be noted that placing ferrite on the driven leg does notsubstantially increase the efiiciency over a structure with no ferriteat all. Thus, a marked increase in efliciency is obtained by mountingferrite toroids on the grounded leg 15.

It is seen that this invention provides a method of substantiallyshortening an antenna while maintaining high efficiency. The ferritemight be Ferramie Q, for example. The ferrite unbalances the current inthe grounded and driven legs to thereby increase the radiation.

Although this invention has been described with respect to particularembodiments thereof, it is not to be so limited, as changes andmodifications may be made therein which are within the spirit and scopeof the invention as defined by the appended claims.

We claim:

1. An antenna structure that can be substantially shortened whilemaintaining high efliciency of radiation comprising a coaxial conductorwith the outer conductor connected to a ground plane, an inner conductorhaving a driven and grounded section coupled by a coupling section andwith the grounded section connected to the ground plane, and a disk ofmagnetic material mounted about the grounded section to substantiallyincrease the efiiciency of radiation.

2. An antenna structure comprising a coaxial conductor with the outerconductor connected to a ground plane, an inner conductor having adriven and grounded section coupled by a coupling section and with thegrounded 3 section connected to the ground plane, and ferrite toroidsmounted about :the grounded section to substantially increase theefficiency of radiation.

4 FOREIGN PATENTS 3/ 1942 Switzerland.

OTHER REFERENCES R f e Cited by h Examiner 5 Noll et 31.: Television andFM Antenna Guide, The MacMillan Company, New York, copyright 1951, pageUNITED STATES PAT ENTS 206 relied on. (Copy in Group 250-5.

2,285,669 6/1942 Lehmann 343-825 2,748,386 5/1956 P olyvd o off HERMANKARL SAALBACH, Przmary Exammer. 3,103,011 9/1963 Seeley 343845 10 R. F.HUNT, Assistant Examiner.

1. AN ANTENNA STRUCTURE THAT CAN BE SUBSTANTIALLY SHORTENED WHILEMAINTAINING HIGH EFFICIENCY OF RADIATION COMPRISING A COAXIAL CONDUCTORWITH THE OUTER CONDUCTOR CONNECTED TO A GROUND PLANE, AN INNER CONDUCTORHAVING A DRIVEN AND GROUNDED SECTION COUPLED BY A COUPLING SECTION ANDWITH THE GROUNDED SECTION CONNECTED TO THE